Machines are known having a deformable diaphragm that is driven by an electromagnetic motor comprising at least a stationary part adapted to channel an electromagnetic flux acting on at least one moving part so as to cause said moving part to move with linear alternating motion in response to alternating variation in the magnetic flux.
By way of example, the machine illustrated in U.S. Pat. No. 6,361,284 comprises a diaphragm disposed between two rigid plates to undulate under the action of an electromagnetic motor in which the moving part is rigidly connected to an edge of the diaphragm so that. alternating motion of the moving part causes the diaphragm to undulate perpendicularly to its plane.
It has been found that such machines emit noise, which even though not of large acoustic power, can nevertheless be troublesome in installations in which the machine is in operation frequently, or even continuously, such as aquariums or refrigerators, for example.
Some of this noise is attributed to the fact that the moving part of the motor, during its alternating motion, drives pulses of air that produce a coherent sound wave.
Furthermore, the moving part presents inertia that is not negligible compared to that of the stationary part. The alternating motion of the moving part thus causes the stationary part to vibrate, thereby in turn causing the support of the machine to vibrate, and constituting an additional source of noise.